Comment to Pete:
Other failure types than EDM do not form an even hardness reduction. It is only the repeated discharge through the oil film that creates millions and billions of small craters and the corresponding hardness reduction (low temperature tempering in SKF parlance). And it is only when you have a reduced hardness that the ball/roller bouncing occurs. Other failure types create other defects in the raceway surfaces. It is only the smooth and "wide area" reduction in hardness that creates bouncing. Just like a dirt road and not a paved road shows a wash-board pattern. The dirt road corresponds, of course, to the surface-tempered raceway.
The paper that Pete refers to says:
"The passage of current causes local surface heating, which leads to lowtemperature
tempering, and accelerates formation of corrugations with time.
The pitch of corrugations on the roller tracks depends on the bearing
kinematics, the frequency of rotation, the position of plane of action of radial
loading, the bearing quality and the lubricant characteristics"
I agree (almost) totally. The "frequency of rotation" (speed in my world) does not seem to be very important - fluting can also be seen in bearings running at variable speed. Winders in paper industry is a good example. Fast winders spend most of their time accelerating and decelerating and they still show very characteristic fluting.
Gunnar Englund
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Half full - Half empty? I don't mind. It's what in it that counts.
